Common-rail fuel injection systems which operate with directly driven injectors are already known. In such injectors, the primary actuator which has a drive according to the piezoelectric principle acts mechanically directly on the nozzle needle of the respective piezoinjector. Owing to mechanical force reactions from the nozzle needle on the actuator, the latter can also be used as a sensor. As a result it is possible to detect precisely the closing time of the nozzle needle and to use it as a controlled variable for the injection quantity of the piezoinjector.
In order to be able to ensure a high level of injection quantity accuracy, there is a need for control of the injection quantity which detects and corrects or compensates component tolerances, wear variables and interference variables, in particular component temperatures, of the piezoinjector.